CHARACTERIZATION OF RAS-DRIVEN HUMAN EPIDERMAL NEOPLASIA. The 2 most common cancers in the U.S., including cutaneous squamous cell carcinoma (SCC), arise from the epidermis. RAS, among the most commonly mutated genes in human cancer, has been implicated in SCC development in mice. The medical relevance of murine studies of SCC and other cancers, however, is limited by major differences between mouse and human skin and by the greater ease of transformation of murine tissues. Recently, we have demonstrated that Ras and CDK4 are induced in a subset of human SCC and that coexpressing Ras with CDK4 induces invasive human epidermal neoplasia indistinguishable from SCC at all levels studied. The overall goal of this proposal is to characterize the mechanistic basis for Ras-driven human epidermal neoplasia as a means of enhancing our understanding of human tissue tumorigenesis. First, we plan to characterize the function of the 3 major proximal Ras effector pathways, Raf, PI3K and RalGEF, in tumorigenesis with CDK4. These effectors can trigger changes found in many cancers, such as proliferation, inhibition of differentiation, angiogenesis and invasion. Ras mutants selective for these pathways as well as the effectors themselves will be used to define their relative contributions to Ras-driven human neoplasia. These studies are designed to define the impacts of individual Ras effector pathways and the degree to which they are necessary and sufficient for initiation of epidermal tumorigenesis. Second, we plan to define the necessity of specific epidermal adhesion proteins in Ras-driven human epidermal neoplasia. Among such adhesion proteins, BP180 and type VI/ collagen are required for epidermal-dermal cohesion in humans and are overexpressed in SCC, however, their potential roles in epidermal cancer are unknown. To address this, will use BP180 and collagen VII-deficient primary human keratinocytes from patients with epidermolysis bullosa _B) in our Ras-driven epidermal cancer model. Determining whether epidermal tumorigenesis can proceed in the absence of BP180 and collagen VII as well as defining the degree to which specific domains of these proteins influence this process will help define their role in human epidermal neoplasia. At the end of the proposed funding period, we hope to have characterized Ras-driven human epidermal neoplasia as a basis for insight into human tissue tumorigenesis and for development of future targeted molecular therapies for cancers of the skin and other organs.